The present invention relates to the art of medical imaging. It finds particular application in conjunction with canceling or correcting for undesired movement especially mechanical movement in C-arm supports for generating three-dimensional computed tomography imaging data, more particularly fluoroscopic x-ray systems, and will be described with particular reference thereto. It is to be appreciated, however, that the invention is also applicable to other diagnostic imaging systems.
In some operating rooms, such as operating rooms for vascular catheter procedures, a projection x-ray imaging device is provided in association with the operating table. More specifically, an x-ray tube or generator and an x-ray detector are mounted on a C-arm which is positioned such that the area of interest or patient lies between the x-ray source and detector. The x-ray source and detector are rotatable and longitudinally displaceable as a unit to select a region and angle for projection imaging. Once the surgeon has positioned the x-ray source and detector in the proper position, the surgeon actuates the x-ray tube sending x-rays through the patient and onto the x-ray detector for a preselected exposure time. The x-rays received by the detector are converted into electronic, video image data representing a projection or shadow-graphic image. The projection or shadow-graphic image is displayed on a video monitor which is viewable by the physician.
In cardiac catheterization procedures, for example, images are generated to show the vasculature system and monitor the advance of the catheter through the blood vessels. More specifically, the surgeon advances the catheter into the patient, stops the surgical procedure, and initiates an x-ray imaging procedure. The x-rays are converted into electronic data and a projection image is displayed.
One of the drawbacks of these x-ray systems is that the resultant image is a projection or shadow-graphic image. That is, the 3-D vasculature system of the patient is projected into a single plane.
If 3-D diagnostic images are required, such images are often taken with a CT scanner or a magnetic resonance imaging device which is typically located in another part of the facility. Thus, any three-dimensional diagnostic images are commonly generated sometime before the surgical procedure starts. Even if a CT scanner is present in the surgical suite, the patient is still moved into the scanner. The transportation of the patient to the CT or MRI machine for further imaging often renders three-dimensional images impractical during many surgical procedures.
However, three-dimensional images obtained are valuable during surgical procedures. After generating a three-dimensional diagnostic image, a surgical procedure is commenced, such as a biopsy. From time to time during the procedure, additional projection diagnostic images are generated to monitor the advancement of the biopsy needle into the patient. The location of the needle can be mathematically predicted from the projection images and monitoring of the physical position of the needle or other instrument can be superimposed on the 3-D diagnostic images. As the needle moves, the superimposed images can be altered electronically to display the needle in the proper position. Various trajectory planning packages have been proposed which would enable the operator to plan the biopsy procedure in advance and electronically try various surgical paths through the three-dimensional electronic data.
Recently, there has been some interest in using relatively low power fluoroscopic systems to generate real time three-dimensional CT reconstructions. Such a technique, disclosed in U.S. Pat. No. 5,841,830 to Barni, et al. is assigned to the assignee of this invention. Barni suggests operating the x-ray tube of a CT scanner in a fluoroscopic mode. Unfortunately, the complete, encircling CT gantry can obstruct access to the surgical site or make that access inconvenient or uncomfortable for the physician.
Another solution disclosed by R. Fahrig, et al. in SPIE Volume 2708 entitled xe2x80x9cCharacterization Of A C-Arm Mounted XRII For 3-D Image Reconstruction During Interventional Neuro Radiologyxe2x80x9d recognizes that a C-arm would provide improved access to the surgical site. The Fahrig article also observes that the C-arm lacks sufficient rigidity to prevent the x-ray source and the detector plates from moving relative to each other, especially during a volume scan where the source and the detector are rotated about an area of interest. Relative motion misaligns the apparatus and causes image degradations. The Fahrig article describes a method wherein the motions and the deflections of the C-arm are premeasured or estimated in pilot scans. The deflections are assumed to remain the same for subsequent scans performed from the same starting point and within all other parameters. System calibration is performed by inserting a three-dimensional phantom containing metal beads or the like with known locations into the imaging field and performing a representative scan. Subsequent image analysis is used to determine positional errors, due to C-arm distortion and deflection. By comparing the detected position of the beads in each image with calculated ideal positions that would occur in the absence of any C-arm distortion, errors for each angular position of the C-arm are calculated. These errors, for each image scan, are stored in a long-term memory and applied to the data collected at corresponding positions of the C-arm, correcting for the calibration errors. Unfortunately, the Fahrig method requires that all volume imaging scans begin in exactly the same location and travel through the same arc. Moreover, any changes in the mechanical characteristics of the C-arm, such as bearing wear, changes in the source to image distance, drive speed, etc., will cause a deterioration in image quality due to the application of improper positional corrections.
The present invention provides a new and improved method and apparatus which overcomes the above-referenced problems and others.
In accordance with the present invention, a diagnostic imaging apparatus includes an x-ray source for transmitting a beam of x-rays through an examination region. An accelerometer is associated with the x-ray source such that a change in linear velocity of the source corresponds to an acceleration reading being registered by the accelerometer.
In accordance with a more limited aspect of the present invention, the diagnostic imaging apparatus includes a second accelerometer for measuring acceleration of the detector.
In accordance with a more limited aspect of the present invention, a position calculator mathematically calculates a position of both the source and the detector from data including signals provided by the accelerometers.
In accordance with a more limited aspect of the present invention, an image reconstruction processor is included to receive a plurality of image data views and for processing the views into a three-dimensional image representation using the calculated position data.
In accordance with a more limited aspect of the present invention, the diagnostic imaging apparatus also includes a collimator movably mounted to the x-ray source for restricting the cone beam of x-rays onto the detector. A misalignment processor receives the position data and controls a drive system mechanically linked to the collimator.
In accordance with another embodiment of the present invention, a radiographic imaging apparatus includes a penetrating radiation source and a radiation receiver. The source and receiver are held in position by a mechanical structure on opposite sides of an examination region. Moreover, the apparatus includes a sensor which detects motion in a selected portion of the mechanical structure and generates a signal in response to that motion. A processor receives the signal from the sensor and calculates a correction required to compensate for at least a portion of the motion detected. The processor then directs the correction calculated to be applied either as a physical correction to the structure or as imaging processing on the received radiation information.
In accordance with another aspect of the present invention, a process for diagnostic imaging includes positioning a radiation source and a receiver relative to an examination region. The process also includes sensing a motion affecting either the source, the receiver, or both and calculating a correction to compensate for the motion. Once the correction has been calculated it is applied either to physically cancel oscillations in a mechanical support before the source transmits a radiation beam; or as imaging processing on the received radiation information after the source transmits a radiation beam.
One advantage of the present invention resides in decreased bulk, or rigidity in the mechanical support needed to resist vibration or motion.
Another advantage of the present invention resides in the acquisition and display of more accurate volumetric images.
Another advantage of the present invention resides in computationally simpler and more efficient image signal manipulation.
Another advantage of the present invention resides in the ability to obtain volume scans from any starting and stopping position.
Another advantage of the present invention resides in the ability to provide dynamic corrections without relying on periodic calibration with three-dimensional phantoms.
Yet other benefits and advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the preferred embodiments.